(1) Field of the Invention
The present invention relates to a technology for playing back a stereoscopic video image and especially to a technology for displaying a stereoscopic video image superimposed with a graphics image.
(2) Description of the Related Art
In recent years, an increasing number of digital contents have been recorded on read-only Blu-ray Discs™, namely, BD-ROM discs. In line with the increase, the use of playback devices conforming to the BD-ROM standard, namely, BD-ROM playback devices, has been spreading at a rapid pace. A content recorded on a BD-ROM disc includes at least one title. The “title” is represented by a combination of application programs, video/audio streams, and image data. The image data represents graphics images of subtitles, a graphics user interface (GUI) and the like, and background images. The video/audio streams and the image data each include a variety of types from which suitable ones can be selected in various playback environments. In particular, the video streams can have a variety of resolutions ranging from 720×480 for the standard definition by the NTSC standard up to 1920×1080 for high definition. For example, when a user specifies a title, the BD-ROM playback device reads application programs corresponding to the title from a BD-ROM disc, and executes the application programs. The application programs cause the BD-ROM playback device to select, from the image data for the title, data suitable for the playback environment, and write the selected data pieces into different plane memories depending on which types the data pieces are; video, graphics, or background. The data stored in the plane memories, namely, planes, are processed in parallel with each other, and then synthesized into one video frame. In this way, the BD-ROM playback device can reproduce appropriate video/audio outputs on various display devices (see, for example, Patent Literature 1).
According to the BD-ROM standard, when the playback device can be connected with an external network such as the Internet, the application programs can cause the playback device to download digital contents from the external network. The contents that can be downloaded include additional contents to the contents recorded on the BD-ROM disc such as bonus video images and subtitles, and interactive contents such as browser screens and games. The application programs can further cause the playback device to display the downloaded subtitles superimposed on the video images being played back from the BD-ROM disc, and display the downloaded browser screen superimposed on the screen on which the video images are displayed. These functions are called “BD-Live”™. As the use of BD-ROM playback devices has been spreading, an increasing number of users have been interested in the BD-Live function.
The spread of the BD-ROM playback devices has also increased the possibility that the display technology of the stereoscopic video images (also referred to as three-dimensional (3D) video images) may be used in homes. The display technology of stereoscopic video images is expected to become a next-generation display technology, and is being developed at a rapid pace. The display technology of stereoscopic video images basically uses the fact that “a person perceives the three-dimensional shape and depth of an object from binocular parallax” (see, for example, Patent Literatures 1 through 3 and Non-Patent Literature 1). More specifically, first, two video frames (namely, a left-view video frame and a right-view video frame) are prepared for one scene. The two video frames slightly differ in the horizontal location and position of the same object. Next, the left-view video frame is projected to the left eye of a viewer, and substantially at the same time, the right-view video frame is projected to the right eye of the viewer. At that time, the viewer perceives the three-dimensional shape and depth of the object from binocular parallax, namely, a slight change in location and position of the object between the frames projected to both eyes of the viewer. Thus, the display technology of stereoscopic video images requires two frames for each scene. Accordingly, stereoscopic video images require a larger amount of data for a fixed display time than monoscopic video images (also referred to as two-dimensional (2D) video images). For this reason, BD-ROM discs and BD-ROM playback devices have an advantage in the display technology of stereoscopic video images.